1. Field of the Invention
The present invention generally relates to a semiconductor device which uses a testing terminal in common as another terminal.
2. Description of the Related Art
Terminals dedicated to tests for internal functions of semiconductor devices such as an IC may be provided. For example, when a thermal shutdown circuit 20 of a regulator IC 100 illustrated in FIG. 1 is checked, the output voltage of a direct-current (DC) power source 30 is applied to a testing terminal 5 to change the input voltage VA of the thermal shutdown circuit 20. When the input voltage VA is changed, the output voltage VB of the thermal shutdown circuit 20 is changed. An output signal Vout is changed when the output voltage VB of the thermal shutdown circuit 20 is changed. Therefore, it is possible to check the thermal shutdown circuit 20 inside the IC by monitoring the output signal Vout output outside the IC from the output terminal 3.
An example of a semiconductor input circuit may use an ordinary terminal as a testing terminal in order to omit the terminal dedicated to testing (Patent Document 1). FIG. 2 is a circuit configuration of the semiconductor input circuit described in Patent Document 1. Referring to FIG. 2, when a test mode is carried out, it is necessary to apply a power source voltage being not ordinarily used to an input terminal 208 which can be used not only as an ordinary terminal but also as a test terminal or more. In this case, because a p-channel MOS transistor 203 connected to the input terminal 208 is turned on and an electric current flows through a resistance element 204, the output signal output from a test mode output terminal 209 changes. By monitoring the output signal from the test mode output terminal 209, it is possible to detect a transition to the test mode.
However, when the resistance value of the resistance element 204 varies, the voltage of the node 207 also varies even when an identical voltage is input to the input terminal 208. Therefore, variation of the resistance value of an internal resistor such as the resistance element 204 greatly influences a result of checking functions of a predetermined internal circuit when an internal voltage such as the voltage of the node 207 is changed by an external input and an output voltage changing in response to the changed internal voltage is monitored to thereby check the functions of the predetermined internal circuit.
Therefore, the object of the embodiments is to provide a semiconductor device which can suppress an influence to a result of checking the internal circuit while providing the testing terminal used in common as another terminal even though there is variation in the resistance value of the internal resistor.    [Patent Document 1] Japanese Laid-open Patent Publication No. Hei. 10-256486